Manufacturing with ESD PEKK

Transcription

1 Manufacturing with ESD PEKK INTRODUCTION Many components in the space, electronics and other industries require surrounding materials to be electrostatic discharge (ESD) safe to prevent damage from static discharge. Stratasys has developed an industry-tailored material for these components using a PEKK (polyetherketoneketone) base resin to combine ESD properties and chemical resistance with suitable mechanical and thermal properties. THE 3D PRINTING SOLUTIONS COMPANY

2 CAPABILITY BACKGROUND Many advanced electronics applications rely on parts that dissipate electrostatic charge buildup. Historically, engineers and material scientists have used various approaches to deal with this buildup of electric potential, including controlling the exit path of the charge or using a material that naturally dissipates the charge buildup. Commerciallyavailable neat thermoplastic resins are normally considered electrically insulating, and are therefore not typically used in applications that are susceptible to electrostatic induction. Additivelymanufactured components, replacing traditionallymachined or metallic versions, offer reduced weight, part cost production and increased design freedom, justifying the cost of change despite not meeting dissipative properties. Under this scenario, several post-processing methods can be used to achieve ESD properties: These techniques achieve electrostatic dissipative control, but additional labor is needed which limits the advantages gained from additive manufacturing. This fostered the development of ESD-compliant thermoplastics such as Stratasys ABS-ESD7. Building on its success, the need for an elevated-temperature, high-performance ESD material was identified. Industry experience with ULTEM 9085 resin and ABS-ESD7 provided insight into effective and desirable material properties. ULTEM 9085 resin has favorable mechanical properties like tensile strength, elongation, and tensile modulus. But it also comes with high post-processing costs to comply with ESD requirements. ABS-ESD7 meets ESD requirements and works well for rapid prototyping and tooling, but cannot be transitioned into the production environment due to insufficient thermal and mechanical properties. 1. Painting or coating to meet resistance requirements 2. Covering with a conductive tape 3. Wrapping with carbon-filled or aluminum-coated films As a new material offering, Stratasys created an ESD PEKK (dissipative polyetherketoneketone) material, combining the favorable properties of both materials. Parts printed from this material are shown in Figure 1. The PEKK base resin meets the necessary structural and temperature requirements and incorporates a conductive filler to meet the dissipative requirement MANUFACTURING WITH ESD PEKK / 2

3 Figure 1 - Avionics box made from ESD PEKK. ( Ω/sq). Although this material formulation was developed in collaboration with the space and electronics industries, it is applicable to the wider market for applications requiring strong mechanical properties, high temperature resistance, ESD control and excellent chemical resistance. many components that require protection from electrostatic charge buildup during launch, orbit and on the production floor. The current FDM (fused deposition modeling) material options either do not meet the stringent outgassing or cleanroom requirements for these applications or need secondary processing to be used for ESD applications. ESD PEKK is a unique material APPLICATION RELEVANCE Ionic charging on spacecraft, electronics, or offering, meeting these requirements without additional post-processing. other components can disrupt or damage critical subsystems and could be detrimental to the entire system if static discharge occurs. Avionics boxes, certain environmental control system ducts, and electronics assembly tooling are some of the MANUFACTURING WITH ESD PEKK / 3

4 MACHINE SETUP Software ESD PEKK is currently available to run on Fortus 3D Printers in a similar manner to that of currentlyavailable materials for these machines. ESD PEKK is an engineered material that has not yet been commercialized by Stratasys and it will run as an R&D material on existing Fortus systems. Purchasing a material software license will enable the R&D material option and the ESD PEKK material parameters will be uploaded to the machine. A custom Insight software parameter file for the R&D material is also needed and can easily be added to existing Insight installations. Enabling the R&D material will not affect current material options or parameters enabled on the machine. Hardware ESD PEKK uses existing, commercially available hardware packages. Both the model and support materials use a T16 tip (shown in Figure 2) and are run through the machine in the same fashion as existing materials. Currently, ESD PEKK has only been tuned for the T16 tip (0.010 in., mm slice height). Development of additional slice heights will be considered if significant demand is identified. Figure 2 - Standard T16 tips used for ESD PEKK. Calibration The nature of the FDM process requires some areas of a part to interface with support material. The additive in this material is sensitive to this interaction and supported surfaces have a slightly higher resistivity value (approximately 1-2 orders of magnitude) than free surfaces, which have resistivity values in the 106 Ω/sq range. This resistivity value increases further when the machine calibration is not taken into consideration. Calibration methods for ESD PEKK differ compared with other materials. Since the material is an R&D material, it is not yet incorporated into the machine controller software or Insight. This necessitates a manual user calibration method. MANUFACTURING WITH ESD PEKK / 4

5 Following the calibration procedure below will reduce the effect of the support interface by making the support layers slightly thinner, which prevents the model material from being imprinted as much by the support, causing resistivity values b) Modify the support Z-offset by in. ( mm). i. For a Fortus 400mc 3D Printer: Enter a in ( mm) Z-offset from the Tip Offset menu (Figure 4). to increase. a) Calibrate the material normally for a T16 tip (support centered at 0-X and 0-Y and support thickness of in. [0.254 mm] as shown in Figure 3). Figure 4 - Z-offset value on a Fortus 400mc. ii. For a Fortus 900mc 3D Printer: Enter a support thickness value of in. (0.330 mm) in the Z-thickness box (Figure 5). This tells the printer that the support thickness is too great and the printer will reduce the tip offset by in. ( mm) in the Z-direction, producing the desired calibration value. Figure 3 - Standard calibration box and Z-thickness calibration. Figure 5 - Z-offset value on a Fortus 900mc 3D Printer. MANUFACTURING WITH ESD PEKK / 5

6 If another calibration box is run, the support thickness value will read ~0.007 in. (0.178 mm) thick instead of in. (0.254 mm) thick. This is expected since the support value was offset by in. ( mm). The machine should be used with this calibration value. hand removal and deleting support material curves from small holes (< 0.25 in. [6.35 mm] Figure 6) in Insight. It will be difficult to remove support by hand from these small holes and they will need to be drilled out after the part is produced if the support is not deleted before building. DESIGN CONSIDERATIONS Supported Faces Following the calibration procedure reduces the range of resistivity values from non-supported to supported areas, but supported faces still have approximately 1-2 orders of magnitude higher Figure 6 - Support in a small hole that will be difficult to remove (left) and support deleted from the hole (right). resistivity values. If this spread is undesirable or if a critical face needs to have a lower resistivity value, designing for additive manufacturing can be used to reduce supported faces. Part orientation can also be manipulated in Insight software to determine which faces interact with the support. Support Removal ESD PEKK uses a unique support material formulated especially for this material. It is a breakaway support system and design considerations for its removal need to be considered and are consistent with other Stratasys materials that use breakaway support. Examples include designing and orienting parts to facilitate MANUFACTURING WITH ESD PEKK / 6

7 Modular Components Some part designs are required to be split for assembly or size reasons. Others may need to be separated later, slide within one another or house other components. These modular components need to be designed with proper clearances in order to fit together properly. A good ruleof-thumb is to use a in. (0.254 mm) total clearance between components as shown in Figure 7. For example, there would be in. on each side of a square or in. radial offset on a circle for a total of inches in each direction or across the diameter. This clearance is designed to be a tight but removable fit and has been found to work for most applications, but it may vary based upon build orientation. Figure 7 - Recommended clearances for modular components. MANUFACTURING WITH ESD PEKK / 7

8 Manufacturing with ESD PEKK MECHANICAL DATA COMPARISONS Figures 8-10 compare common material properties between ABS-ESD7, the current ESD offering with an ABS base resin; ESD PEKK, the new ESD material offering using a PEKK base resin; and ULTEM 9085 resin, one of the most widely used materials for FDM aerospace production parts. Figure 8 - Comparison of ABS-ESD7 and ULTEM 9085 resin to ESD PEKK in the on-edge build direction. Figure 9 - Comparison between ABS-ESD7, ESD PEKK, and ULTEM 9085 resin mechanical properties in the vertical build direction. MANUFACTURING WITH ESD PEKK / 8

9 Figure 10 - Surface resistivity and heat deflection temperature comparisons between ABS-ESD7, ESD PEKK, and ULTEM 9085 resin. To explore your own custom material development program to meet your unique 3D printing challenges, contact AdvancedMaterials@Stratasys.com. MANUFACTURING WITH ESD PEKK / 9

10 STRATASYS.COM HEADQUARTERS 7665 Commerce Way, Eden Prairie, MN (US Toll Free) (Intl) (Fax) 2 Holtzman St., Science Park, PO Box 2496 Rehovot 76124, Israel (Fax) THE 3D PRINTING SOLUTIONS COMPANY ISO 9001:2008 Certified 2015, 2016 Stratasys. All rights reserved. Stratasys, Stratasys signet, FDM and Fortus are registered trademarks of Stratasys Inc. Fortus 400mc, Fortus 900mc, Insight and ABS-ESD7 are trademarks of Stratasys, Inc. ULTEM is a registered trademark of SABIC or affiliates. All other trademarks are the property of their respective owners, and Stratasys assumes no responsibility with regard to the selection, performance, or use of these non-stratasys products. Product specifications subject to change without notice. Printed in the USA. WP_FDM_ManufacturingEDS-PEKK_A4_0216 For more information about Stratasys systems, materials and applications, call or visit